Performance Evaluation of Phenol-Resin-Based Adsorbents for Heat Transformation Applications

Phenol resins (PRs) are considered as relatively inexpensive adsorbents synthesized from agricultural biomass via employing a variety of synthesized procedures. The performance of PR for heat transformation application is not widely investigated. In this regard, the present study aims to evaluate the four PR derivative/refrigerant pairs, namely (i) KOH6-PR/CO2, (ii) SAC-2/HFC, (iii) KOH4-PR/ethanol, and (iv) KOH6-PR/ethanol, for adsorption cooling and adsorption heating applications. Ideal cycle analyses and/or thermodynamic modelling approaches were utilized comprising governing heat and mass balance equations and adsorption equilibrium models. The performance of the AHP system is explored by means of specific cooling energy (SCE), specific heating energy (SHE), and coefficient of performance (COP), both for cooling and heating applications, respectively. It has been realized that KOH6-PR/ethanol could produce a maximum SCE of 1080 kJ/kg/cycle and SHE of 2141 kJ/kg/cycle at a regeneration temperature (Treg) and condenser temperature (Tcond) of 80 °C, and 10 °C, respectively, followed by KOH4-PR/ethanol, SAC-2/HFC-32, and KOH6-PR/CO2. The maximum COP values were estimated to be 1.78 for heating and 0.80 for cooling applications, respectively, at Treg = 80 °C and Tcond = 10 °C. In addition, the study reveals that, corresponding to increase/decrease in condenser/evaporator pressure, both SCE and SHE decrease/increase, respectively; however, this varies in magnitude due to adsorption equilibrium of the studied PR derivative/refrigerant pairs.


Introduction
Research activities are shifting toward the development of energy-efficient solid sorption, namely adsorption heat pump (AHP) systems, which are acknowledged as a credible route for minimizing the exponential growth in energy demand in the air conditioning (AC) sector. Mechanical vapor compression (MVC) AC systems have a high coefficient of performance (COP) ranging between 3.0 and 5.0, consequently indicating their wide implementation as a convenient commercialized cooling/heating system [1,2]. However, environmental consequences aligned with the MVC-AC system include high global warming potential, emission of harmful greenhouse gasses, destruction of the ozone layer, and prominently alleviating the paucity of natural fossil fuel reserves [3]. On the other hand, deterioration over time, and low hydro-thermal stability, hindering their wider implementation. Significant research efforts are directed towards the advancement of MOFs, with a particular focus on enhancing their adsorption capabilities and optimizing their thermophysical properties [38,39]. A low-cost sustainable adsorbent is principally required to develop an energy-efficient AHP system.
Phenol resin (PR) is another adsorbent class manufactured from agriculture biomass for various heat transformation applications. El-Sharkawy et al. [40] developed two PR derivatives activated with potassium hydroxide (KOH), namely KOH4-PR and KOH6-PR, in communication with ethanol as a refrigerant from the perspective of developing a nextgeneration AC system. In this regard, the isothermal characterization was performed using thermogravimetric analysis. In addition, adsorption isotherm modeling was performed using a Dubinin-Astakhov (D-A) model. The results indicated that the KOH6-PR is capable of uptake of 2 kg of ethanol per kg of KOH6-PR and 1.43 kg of ethanol per kg of KOH4-PR. Uddin et al. [41] investigated CO 2 adsorption on KOH6-PR. The results reveal that the KOH6-PR ethanol can uptake 1.69 kg of CO 2 per kg of KOH6-PR. Sultan et al. [42] investigated the adsorption of HFC-32 on spherical activated carbon (SAC-2) and reported uptake of 2.34 kg/kg. These PR derivative/refrigerant pairs could outperform if employed in the AHP system due to their porosity and adsorption potentials.
In this realm, the present study aims to investigate the performance of four kinds of phenol resin (PR) derivative/refrigerant pairs abbreviated as (i) KOH6-PR/CO 2 , (ii) SAC-2/HFC-32, (iii) KOH4-PR/ethanol, and KOH6-PR/ethanol for an AHP system that mutually exhibited adsorption cooling and adsorption heating applications. To the best of the author's knowledge, the selected PR derivative/refrigerant pairs have not been investigated for twin applications. The thermophysical properties and fitting constants of the adsorption isotherm model for the selected PR derivative/refrigerant pairs are available via [40][41][42] and utilized accordingly in the present research. A steady-state thermodynamic modeling scheme is utilized comprising the Dubinin-Astakhov model, and the system's governing heat and mass balance equations are widely accessible and often employed in the literature [43,44]. The key performance indicators of the AHP system, including specific cooling energy (SCE), specific heating energy (SHE), and COP, are evaluated at steady-state conditions. Furthermore, the study also performs a sensitivity analysis in order to explore the effect of regeneration temperature (T reg ), adsorption temperature (T ads ), condenser pressure (P cond ), and evaporator pressures (P evap ) on the studied key performance indicators of the AHP system. Overall, the study contributes positively regarding the selection of the potential PR derivative/refrigerant pair for the AHP system.

Adsorption Heat Pump (AHP)
The working of AHP follows a close cyclic configuration, employing well-known thermodynamic processes, i.e., adsorption, isosteric heating, regeneration, and isosteric cooling, respectively. Generally, the AHP system contains an expansion valve, heating/cooling water baths, and four cylinders retrofitted with heat exchangers. Two cylinders within the AHP device are packed with porous adsorbent material, while the remaining two cylinders serve as an evaporator and condenser, respectively. Indeed, the performance of the AHP system relies heavily on the type of adsorbent material, associated adsorption equilibrium, as well as thermophysical properties. The working schematic and ideal cycle of the AHP system are showcased in Figure 1 (left) and (right), respectively. The thermodynamic processes are accomplished in the cylinders packed with the porous adsorbent material; however, they have been controlled/regulated with the externally connected heating/cooling water baths in order to maintain the required thermal fronts. For instance, to facilitate the adsorption process, a cooling bath is connected from the perspective of harnessing adsorption heat released during the process, thereby augmenting the overall adsorption capacity. During the adsorption process, the refrigerant undergoes a transition from liquid to vapor within the evaporator via utilizing surrounding heat. Subsequently, the vapor is effectively trapped within the pore spaces of the adsorbent material, facilitated by the establishment of Van der Waals forces of interaction and driven by significant affinity between the refrigerant and the adsorbent. As the adsorption process is performed at constant evaporator pressure, it is thereby termed as isobaric adsorption. Similarly, for enabling the desorption process, an external heating source is required (i.e., heating bath), causing the breakdown of the Van der Waals force of attraction. As a result, the refrigerant molecules are liberated from the adsorbent pore spaces under conditions of high temperature and pressure and subsequently proceed towards the condenser. The coolant circulating inside the condenser heat exchanger captures the latent heat of the refrigerant and supports the refrigerant phase transition. A high-pressure liquid with relatively lowtemperature refrigerant is produced, which is then directed to the expansion valve. The expansion valve undergoes the refrigerant to experience a sudden drop in pressure, leading to a corresponding decrease in temperature. As a result, a low-pressure liquid-vapor mixture is generated, which is then directed to the evaporator to initiate the subsequent cycle. Prior to the adsorption and desorption processes, isosteric cooling and isosteric heating processes are conducted with the aim of adjusting the cylinder pressure to match the pressure of the condenser and evaporator, respectively. Both processes, also known as switching times, allow the cylinder to prepare itself for the subsequent adsorption and desorption processes by increasing or decreasing the pressure accordingly. The isosteric heating temperature (T iso_heating ) and isosteric cooling temperature (T iso_cooling ) are the intermediate temperatures values beyond which the desorption and adsorption processes are executed, respectively. The extended details relevant to the determination of these temperature points are provided in Section 4. transition from liquid to vapor within the evaporator via utilizing surrounding heat. Subsequently, the vapor is effectively trapped within the pore spaces of the adsorbent material, facilitated by the establishment of Van der Waals forces of interaction and driven by significant affinity between the refrigerant and the adsorbent. As the adsorption process is performed at constant evaporator pressure, it is thereby termed as isobaric adsorption. Similarly, for enabling the desorption process, an external heating source is required (i.e., heating bath), causing the breakdown of the Van der Waals force of attraction. As a result, the refrigerant molecules are liberated from the adsorbent pore spaces under conditions of high temperature and pressure and subsequently proceed towards the condenser. The coolant circulating inside the condenser heat exchanger captures the latent heat of the refrigerant and supports the refrigerant phase transition. A high-pressure liquid with relatively low-temperature refrigerant is produced, which is then directed to the expansion valve. The expansion valve undergoes the refrigerant to experience a sudden drop in pressure, leading to a corresponding decrease in temperature. As a result, a low-pressure liquid-vapor mixture is generated, which is then directed to the evaporator to initiate the subsequent cycle. Prior to the adsorption and desorption processes, isosteric cooling and isosteric heating processes are conducted with the aim of adjusting the cylinder pressure to match the pressure of the condenser and evaporator, respectively. Both processes, also known as switching times, allow the cylinder to prepare itself for the subsequent adsorption and desorption processes by increasing or decreasing the pressure accordingly. The isosteric heating temperature (Tiso_heating) and isosteric cooling temperature (Tiso_cooling) are the intermediate temperatures values beyond which the desorption and adsorption processes are executed, respectively. The extended details relevant to the determination of these temperature points are provided in Section 4. The AHP device can potentially be used both for both cooling and heating applications. The cooling potential (Qevap) is realized in the AHP cycle during the evaporation of refrigerant in the evaporator, whereas the heating potential is realized during condensation (Qcond) and adsorption (Qads) processes. The steady-state operating conditions of the AHP system used for the present study are summarized in Table 1. The AHP device can potentially be used both for both cooling and heating applications. The cooling potential (Q evap ) is realized in the AHP cycle during the evaporation of refrigerant in the evaporator, whereas the heating potential is realized during condensation (Q cond ) and adsorption (Q ads ) processes. The steady-state operating conditions of the AHP system used for the present study are summarized in Table 1.

Materials
In this study, four kinds of PR derivative/refrigerant pairs, i.e., (i) KOH6-PR/CO 2 [41], (ii) SAC-2/HFC-32 [42], (iii) KOH4-PR/ethanol [40], and (iv) KOH6-PR/ethanol [40], are studied from the viewpoint of thermodynamically analyzing their performances for AHP system exhibiting both adsorption cooling and heating applications. The comprehensive discussion and procedure regarding the manufacturing as well as thermophysical features and structures of the PR derivatives can be found from the cited literature [40][41][42].
A quick overview regarding the synthesizing of the studied PR derivatives in order to encompass all facets is as follows [44][45][46]: PR derivatives were prepared via carbonization of the raw PR occurring at 600 • C for an hour at a heating rate of 5 • C/min in the presence of nitrogen (N 2 ) flow. For activation, KOH was utilized as activating agent. Two weight ratios (KOH/carbonized PR) of 4 and 6 were subjected to heat treatment process at a heating rate of 5 • C/min and maintained at 900 • C for one hour under N 2 flow. To eliminate the salts generated during the heat treatment and residual KOH, the samples underwent a rigorous washing procedure. This involved subjecting them to multiple rinses with a HCl solution and a subsequent rinse with deionized water for a pH of 7. The collected sample was subjected to two-step drying process. Primary drying takes place at 100 • C for three hours while secondary drying takes place at 150 • C for 12 h. Figure 2 shows the pictorial of raw PR, entailing SEM images of raw PR and associated derivatives. The porous properties, elemental composition, and thermal properties of the PR derivatives are presented in Table 2 [40][41][42].
A quick overview regarding the synthesizing of the studied PR derivatives in orde to encompass all facets is as follows [44][45][46]: PR derivatives were prepared via carboniza tion of the raw PR occurring at 600 °C for an hour at a heating rate of 5 °C/min in th presence of nitrogen (N2) flow. For activation, KOH was utilized as activating agent. Tw weight ratios (KOH/carbonized PR) of 4 and 6 were subjected to heat treatment process a a heating rate of 5 °C/min and maintained at 900 °C for one hour under N2 flow. To elim inate the salts generated during the heat treatment and residual KOH, the samples under went a rigorous washing procedure. This involved subjecting them to multiple rinses wit a HCl solution and a subsequent rinse with deionized water for a pH of 7. The collected sample was subjected to two-step drying process. Primary drying takes place at 100 °C fo three hours while secondary drying takes place at 150 °C for 12 h. Figure 2 shows th pictorial of raw PR, entailing SEM images of raw PR and associated derivatives. The po rous properties, elemental composition, and thermal properties of the PR derivatives ar presented in Table 2 [40][41][42].

Thermal Property
Specific heat capacity (kJ/kg.K) N/A 0.751-0.924 (@ 30-150 • C) [45] N/A A thermodynamic model based on the adsorption equilibrium model and governing heat and mass balance equations are utilized and/or programmed in Python from the perspective of investigating the PR derivative/refrigerant pairs for the AHP system. The developed Python program is capable of estimating the heating and cooling potentials of AHP corresponding to different operating conditions (i.e., regeneration and adsorption temperature). In addition, the effect of evaporator and condenser pressure is analyzed for each PR derivative/refrigerant pair. The subsequent subsections entail the specifics of the adsorption equilibrium model as well as a comprehensive discussion regarding the thermodynamic equations and Python libraries used in this study.

Adsorption Equilibrium
Dubinin-Astakhov (D-A) isotherm model is used for simulation of the adsorption isotherms. The well-optimized fitting constants for the D-A model corresponding to each PR derivative/refrigerant pair are provided in Table 3 and available via [40][41][42]. The D-A isotherm model is presented in Equation (1) as provided by [46]: where w (kg ref /kg PR or cm 3 /g ref ) and wo (kg ref /kg PR ) are the adsorption equilibrium and maximum adsorption uptake possessed by the PR derivatives corresponding to the different refrigerants, T (K) is adsorption temperature, E (kJ/kg) is the characteristic energy, and n is the structural heterogeneity parameter commonly named as D-A fitting constant. P and Ps are the partial and saturation pressures (kPa), respectively. The P s of the refrigerants corresponding to T are obtained from the Coolprop, an open-source Python library for fluid properties. However, beyond the critical temperature (T > T cr ) of the refrigerants, the P s values are calculated from the pseudo-saturation pressure provided by Equation (2) [41].
In addition, q is evaluated on volumetric bases (cm 3 ref /g PR ) to convert into equilibrium adsorption amount (kg ref /kg PR ) using Equation (3) as provided by [41,42]: Materials 2023, 16, 5262 In Equation (2), P c is the critical pressure and k is a fitting constant. The k values for HFC-32 and CO 2 are provided in Table 3 [41,42]. However, V t is the molar volume of the refrigerant determined by Equation (3) using the Refprop software at triple point temperature (T t ). The α is the thermal expansion coefficient taken as 0.0025 K −1 . The V t value of HFC-32 and CO 2 refrigerants are computed as 0.69966 cm 3 /g ref and 0.84858 cm 3 /gref, respectively.

System Governing Equations
In this section, steady-state governing heat and mass balance equations used in ongoing research are presented and discussed accordingly in order to develop a Python program that is employed to evaluate the performance of the AHP system. A generalized programming code is written in Python for thermodynamic modeling of the AHP system, which is capable of investigating different adsorbent/refrigerant pairs. The scope of the work in this case, however, is confined to analyzing the PR derivative/refrigerant pairs. Clausius-Clapeyron model is utilized for determining the heat of adsorption/desorption (Q st ), provided by Equation (4) [41]. Accordingly, isosteric heating temperature (T iso_heating ) and isosteric cooling temperature (T iso_cooling ) were estimated.
Once isosteric temperature points are identified, the Python program developed pressure-temperature-uptake (P-T-U) diagram. Four thermodynamic processes, namely (i) isobaric adsorption, (ii) isosteric heating, (iii) isobaric desorption, and (iv) isosteric cooling processes, perform in sequence to complete a single AHP cycle. The time required to complete a single AHP cycle depends upon the adsorption kinetics. However, the primary objective of the present study is to undertake a comprehensive investigation into steady-state phenomena. It is noteworthy that, within the scope of this research, the kinetics pertaining to PR derivative/refrigerant pairs have deliberately been excluded from consideration. Thermodynamic processes involved in the AHP cycle are provided by Equations (5)-(8) [43,47].
Isobaric adsorption (process 1-2); Isosteric heating (process 2-3); Isobaric desorption (process 3-4); Isosteric cooling (process 4-1); The first term in Equation (5) computes the sensible heat release during the cooling of PR derivative, whereas the second term computes the latent heat release during the adsorption of refrigerant vapors. The total energy release during isobaric adsorption (Q 1-2 ) is indicated with a negative sign. The total isosteric heat (Q 2-3 ) supplied for increasing the temperature from T 2 to T 3 is computed by Equation (6), which is the summation of the sensible heat gained by the PR derivative adsorbent and heat gained by the refrigerant vapors under equilibrium conditions. The desorption heat is supplied from the external lowgrade heat source. The heat supplied during isobaric desorption (Q 3-4 ) can be computed from Equation (7). The first term calculates the sensible heat supplied to the PR derivative adsorbent for reaching regeneration temperature (T 4 ), whereas the second term is the latent heat gained by refrigerant vapors for desorbing from the adsorbent surface. Again, the heat is released during the isosteric cooling process (Q 1-4 ) estimated by Equation (8) that is the summation of the two sensible heats for lowering the temperature of PR derivative as well as the refrigerant vapors that still adsorb on the surface. The key performance indicators for both adsorption cooling and adsorption heating are estimated using Equations (9)-(13) as provided by [43,47]: Evaporator/specific cooling energy (SCE): Condenser; Q cond = (w max − w min ) m PRd LH vap@T cond (10) Specific heating energy (SHE); Coefficient of performance for cooling application (COP cooling ); Coefficient of performance for heating application (COP heating ); The specific cooling energy (SCE) or Q evap is obtained during the isobaric adsorption process when the refrigerant in the evaporator changes from liquid to vapors by gaining the surrounding heat. In order to compute the refrigeration effect, Equation (9) is utilized, which consists of latent heat of evaporation of the refrigerant minus the sensible heat of refrigerant, which enters into the evaporator at condenser temperature. Similarly, the specific heating energy (SHE) obtained from the single AHP cycle is the function of heat released during condensation plus the heat released during the isosteric cooling and isobaric adsorption. The condenser (Q cond ) is computed by the latent heat of vaporization at condenser temperature, as provided in Equation (10). The total SHE is calculated from Equation (11). The COP for both cooling and heating is provided by Equations (12) and (13), respectively. adsorption. The condenser (Qcond) is computed by the latent heat of vaporization at condenser temperature, as provided in Equation (10). The total SHE is calculated from Equation (11). The COP for both cooling and heating is provided by Equations (12) and (13), respectively.

KOH6-PR/CO2
The ideal cycle and/or P-T-U for KOH6-PR/CO2 is presented in Figure 4a, determined at operating conditions provided in Table 1. The Tiso_heating and Tiso_cooling were computed at 54.90 °C and 52.95 °C, respectively. The net adsorption uptake of ethanol on KOH6-PR is estimated to be 0.525 kg/kg at the operational states provided in Table 1. Figure 4b presents the simulated adsorption equilibrium profiles of KOH6-PR/CO2 at the temperature range from 10 °C to 100 °C regarding superimposing the AHP cycle. The reference study [41] experimentally investigated the adsorption equilibrium profiles at temperatures of 20 to 70 °C with an interval of 5 °C, and 10 °C, and estimated the fitting constants for the DA model. However, in the present study, the same fitting constants were utilized to simulate the adsorption isotherms at temperatures less than and greater than 20 °C and 70 °C, respectively. The Pevap and Pcond are assumed to be 4629.83 kPa and 6941.10 kPa, respectively, based on the saturation pressure of CO2. Figure 4c shows the effect of Treg from 50 °C to 80 °C on specific energies and COPs that can be obtained from the

KOH6-PR/CO 2
The ideal cycle and/or P-T-U for KOH6-PR/CO 2 is presented in Figure 4a, determined at operating conditions provided in Table 1. The T iso_heating and T iso_cooling were computed at 54.90 • C and 52.95 • C, respectively. The net adsorption uptake of ethanol on KOH6-PR is estimated to be 0.525 kg/kg at the operational states provided in Table 1. Figure 4b presents the simulated adsorption equilibrium profiles of KOH6-PR/CO 2 at the temperature range from 10 • C to 100 • C regarding superimposing the AHP cycle. The reference study [41] experimentally investigated the adsorption equilibrium profiles at temperatures of 20 to 70 • C with an interval of 5 • C, and 10 • C, and estimated the fitting constants for the DA model. However, in the present study, the same fitting constants were utilized to simulate the adsorption isotherms at temperatures less than and greater than 20 • C and 70 • C, respectively. The P evap and P cond are assumed to be 4629.83 kPa and 6941.10 kPa, respectively, based on the saturation pressure of CO 2 . Figure 4c shows the effect of T reg from 50 • C to 80 • C on specific energies and COPs that can be obtained from the KOH6-PR/CO 2 pair. It has been observed that, corresponding to an increase in T reg , the SCE and SHE linearly increase. At T reg of 80 • C, the SCE and SHE approach to a maximum potential with a magnitude of 77.44 and 314.58 KJ/kg/cycle. In accordance with increasing the T reg from 51 to 80 • C, the COP for AHP for heating application varies from 0.95 to 1.07, which depicts an increasing trend. However, regarding AHP for cooling application, it has been identified that the COP drops from 0.28 to 0.26. On the other hand, corresponding to an increase in T ads , specific energy and COP both for heating and cooling applications are linearly decreased, as shown in Figure 4d. The SCE and SHE were estimated at 88 and 320 kJ/kg/cycle, respectively. Similarly, at T ads of 30 • C, the COP heating was estimated at 4.0-fold higher as compared to the COP cooling . Figure 4e shows the effect of P cond on both SCE and SHE at T reg of 52 • C, 63 • C, and 80 • C, differentiated with markers. In the case of the SCE, the P cond was observed to be sensitive to both P cond and T reg . However, for SHE, relatively small variation is observed corresponding to an increase in the P cond , while there was significant improvement with respect to the step-based increment in T reg . This implies that the influence of the P cond is unremarkable on SHE for the KOH6-PR/CO 2 pair. The maximum SCE of 175 kJ/kg/cycle and SHE of 340 kJ/kg/cycle are observed at P cond and T reg of 4525 kPa and 80 • C, respectively. Similarly, the SCE and SHE are observed to be sensitive and insensitive to P evap , respectively, as shown in Figure 4f. However, T cool significantly enhances the magnitude of both SCE and SHE. The maximum SCE of 165.40 kJ/kg/cycle and SHE of 340 kJ/kg/cycle were observed at P evap = 6360 kPa and T cool of 30 • C. Figure 4g,h show the detailed impact of T cond , varying from 10 to 25 • C, and T reg from 51 to 80 • C at T evap = 10 • C on both SCE and SHE for developing better understanding as well as visualization of the trends. It can be concluded that the impact of T cond is highly sensitive for SCE, whilst T cond does not significantly impact the SHE at T reg > 75 • C. The extended results regarding the influence of operating parameters on the SCE, SHE, COP cooling , and COP heating are provided in Appendix A accordingly.  Table 1. The T iso_heating and T iso_cooling were computed to be 54.90 • C and 52.95 • C, respectively. The net absorption uptake of HFC-32 on SAC-2 adsorbent was estimated to be 0.669 kg/kg. Figure 5b presents the simulated adsorption equilibrium profiles corresponding to variations in adsorption/desorption temperature, superimposed with the ideal AHP cycle. The isobaric adsorption and isobaric desorption processes are taking place at 1030.44 kPa and 1979.49 kPa for P evap and P cond , respectively. Figure 5c presents the SCE and SHE obtained from SAC-2/HFC-32. The SCE found 175.20 kJ/kg/cycle, whereas SHE was 561.14 kJ/kg/cycle. Similarly, the COP cooling varied from 0.50 to 0.45, whereas the COP heating was estimated at 1.24 to 1.46, corresponding to the increase in the T reg from 50 to 80 • C. On the other hand, corresponding to the increment in T ads from 30 to 55 • C, the SCE and SHE decrease from 200 to 0 kJ/kg/cycle and from 590 to 0 kJ/kg/cycle, thereby recommending the 30 • C optimum T ads for the AHP system. Figure 5e presents the impact of P cond on SCE and SHE while maintaining P evap = 1030.44 kPa. It has been observed that the P cond responds to a linear decrease in SCE and SHE; however, the higher P evap responds to a linear increase in both SCE and SHE, as shown in Figure 5f. It is noteworthy that both P evap and P cond have a significant influence on the performance of the AHP system packed with SAC-2/HFC-32 pair. Figure 5g and (h) show the detailed impact of T cond varying from 10 to 25 • C and T reg from 51 to 80 • C at T evap = 10 • C on both SCE and SHE for developing better understanding as well as visualization of the trends. It can be concluded that the impact of T cond as well as T reg is highly sensitive for both SCE and SHE. The extended results regarding the influence of operating parameters on the SCE, SHE, COP cooling , and COP heating are provided in Appendix A accordingly.  processes are taking place at 1030.44 kPa and 1979.49 kPa for Pevap and Pcond, respectively. Figure 5c presents the SCE and SHE obtained from SAC-2/HFC-32. The SCE found 175.20 kJ/kg/cycle, whereas SHE was 561.14 kJ/kg/cycle. Similarly, the COPcooling varied from 0.50 to 0.45, whereas the COPheating was estimated at 1.24 to 1.46, corresponding to the increase in the Treg from 50 to 80 °C. On the other hand, corresponding to the increment in Tads from 30 to 55 °C, the SCE and SHE decrease from 200 to 0 kJ/kg/cycle and from 590 to 0 kJ/kg/cycle, thereby recommending the 30 °C optimum Tads for the AHP system.

KOH4-PR/Ethanol
The ideal cycle and/or P-T-U for KOH4-PR/ethanol is presented in Figure 6a, determined at operating conditions provided in Table 1. The T iso_heating and T iso_cooling were computed to be 51.95 • C and 56.12 • C, respectively. The net adsorption uptake of ethanol on KOH4-PR is estimated to be 0.727 kg/kg at the operational states provided in Table 1. Figure 6b presents the simulated adsorption equilibrium profiles of KOH4-PR/ethanol at a temperature range from 10 • C to 100 • C regarding superimposing the AHP cycle. It is noteworthy that the fitting constants of the adsorption equilibrium were computed for the temperature range between 30 and 70 • C [40]. However, for higher temperatures (>70 • C) and lower temperatures (<30 • C), the adsorption uptakes are simulated using the D-A model varying the temperature parameter. Based on the saturation properties of the ethanol, the P evap and P cond are assumed to be 3.11 kPa and 10.41 kPa, respectively. Figure 6c shows the effect of T reg from 50 • C to 80 • C on specific energies and COPs that can be obtained from the KOH4-PR/ethanol pair. It has been observed that, corresponding to increase in T reg , the SCE and SHE linearly increase. At T reg of 80 • C, the SCE and SHE approach maximum potential, with values of 643.85 and 1474.12 KJ/kg/cycle, entailing maximum COP of 1.78 and 0.79, respectively. On the other hand, it corresponds to an increase in T ads , with both specific energy and COP both for heating and cooling applications linearly decreasing, as shown in Figure 6d. This implies that the T reg = 80 • C and T ads = 30 • C are supportive in order to obtain the maximum potential (either cooling or heating) from the KOH4-PR/ethanol. Figure 6e shows the effect of P cond on both SCE and SHE at T reg of 52 • C, 63 • C, and 80 • C, differentiated with markers. The study reveals that P cond of 3.11 kPa and T reg of 80 • C is promising in terms of producing high SCE (980 kJ/kg/cycle) and SHE (1790 KJ/kg/cycle). The increment in the T reg reflects the step-based improvement in both SCE and SHE, whilst the degraded corresponds to an increase in P cond . Figure 6f shows the effect of P evap and T cool on SCE and SHE. The results depict that nearly linear increments of SCE and SHE correspond to an increase in P evap . Also, the step-based increment reflects the significant improvement in the overall SCE and SHE. The maximum SCE of 960 kJ/kg/cycle and SHE of 1750 kJ/kg/cycle were computed at P evap of 7.85 kPa and T cool of 30 • C. Figure 6g,h show the detailed impact of T cond , varying from 10 to 25 • C and T reg from 51 to 80 • C at T evap = 10 • C on both SCE and SHE for developing better understanding as well as visualization of the trends. It can be concluded that the impact of T cond on both SCE and SHE is ignorable at T reg > 70 • C. The extended results regarding the influence of operating parameters on the SCE, SHE, COP cooling , and COP heating are provided in Appendix A accordingly.

KOH6-PR/Ethanol
The ideal cycle and/or P-T-U for KOH6-PR/ethanol is presented in Figure 7a, determined at operating conditions provided in Table 1. The T iso_heating and T iso_cooling were computed to be 51.97 • C and 56.10 • C, respectively. The net adsorption uptake of ethanol on KOH6-PR is estimated at 1.0265 kg/kg at the operational states provided in Table 1. Figure 7b presents the simulated adsorption equilibrium profiles of KOH6-PR/ethanol at a temperature range from 10 • C to 100 • C entailing superimposing the AHP cycle. The cited study determined the fitting constants for KOH6-PR/ethanol at a temperature range between 30 and 70 • C [40]; however, in the present study, the adsorption isotherms for higher temperatures (>70 • C) and lower temperatures (<30 • C) are estimated using the D-A model varying the temperature parameter. The P evap and P cond assume 3.11 kPa and 10.41 kPa, respectively. Figure 7c shows the effect of T reg from 50 • C to 80 • C on specific energies and COPs that can be obtained from the KOH6-PR/ethanol pair. It has been observed that, corresponding to an increase in T reg , the SCE and SHE linearly increase. At T reg of 80 • C, the SCE and SHE approach to a maximum potential with a magnitude of 907.77 and 2024.34 KJ/kg/cycle, with maximum COP of 0.79 and 1.78, respectively. In the case of AHP for cooling application, the COP followed a declining trend (0.84 to 0.78) due to the mounting of externally supplied heat that leads to a slight drop in the COP. On the other hand, it corresponds to an increase in T ads -specific energy and COP both for heating and cooling applications, which follow a relatively curved shape declining trend, as shown in Figure 7d. The SCE and SHE were estimated at 915.00 and 2032.72 kJ/kg/cycle, respectively. Similarly, at T ads of 30 • C, the COP for heating application was estimated 2.34-fold higher as compared to the COP for cooling application. Figure 7e shows the effect of P cond on both SCE and SHE at T reg of 52 • C, 63 • C, and 80 • C, differentiated with markers. The study reveals that P cond of 3.11 kPa and T reg of 80 • C are promising in terms of producing high SCE (1033.78 kJ/kg/cycle) and SHE (2235 KJ/kg/cycle). However, it has been identified that, at T reg = 80 • C, the P cond seems unresponsive to producing SHE for KOH6-PR/ethanol. Similarly, the slope of the SCE profiles corresponds to an increase in the T reg from 52 • C to 80 • C. Figure 7f shows the effect of P evap , and T cool on SCE and SHE. The maximum SCE of 1664.21 kJ/kg/cycle and SHE of 2736 kJ/kg/cycle were estimated at P evap of 7.85 kPa and T cool of 30 • C. Figure 7g,h show the detailed impact of T cond , varying from 10 to 25 • C and T reg from 51 to 80 • C at T evap = 10 • C on both SCE and SHE for developing better understanding as well as visualization of the trends. It can be concluded that the impact of T cond on both SCE and SHE is ignorable at T reg > 75 • C. The extended results regarding the influence of operating parameters on the SCE, SHE, COP cooling , and COP heating are provided in Appendix A accordingly.

Conclusions
The global transition towards the development of energy-efficient air conditioning systems encourages field researchers to explore the potential of an adsorption heat pump (AHP) system for heat transformation applications. Adsorbent/refrigerant pairs play an important role in the success of the AHP system. In this realm, the study aims to evaluate four kinds of phenol resin (PR) derivative/refrigerant pairs, i.e., (i) KOH6-PR/CO 2 , (ii) SAC-2/HFC, (iii) KOH4-PR/ethanol, and (iv) KOH6-PR/ethanol, for adsorption cooling and adsorption heating applications. A steady-state thermodynamic modeling strategy is utilized containing a Dubinin-Astokhov (D-A) model and governing heat and mass balance equations to explore the performance of the AHP system for the selected PR derivative/refrigerant pairs. Specific cooling energy (SCE), specific heating energy (SHE), and associated coefficient of performances (COP) are estimated in response to influential operating parameters, i.e., regeneration temperature (T reg ), adsorption temperature (T ads ), condenser pressure (P cond ), and evaporator pressure (P evap ). The analysis reveals that KOH6-PR/ethanol outperforms for the AHP system due to producing the highest SCE of 907.77 kJ/kg/cycle, with SHE of 2024.34 kJ/kg/cycle at T reg of 80 • C, P cond of 10.41 kPa, and P evap of 3.106 kPa, followed by KOH4-PR/ethanol, SAC-2/HFC-32, and KOH6-PR/CO 2 . Accordingly, the COP cooling and COP heating were estimated to be 0.79, and 1.78, respectively. In addition, for KOH6-PR/ethanol, it was observed that condenser temperature (T cond ) and evaporator temperature (T evap ) have no and/or relatively less sensitive for higher T reg (>75 • C) and lower T ads (<32 • C), respectively. However, prior to implementation, meticulous consideration of the adsorption kinetics is highly imperative. Therefore, the performance of the KOH6-PR/ethanol pair may exhibit considerable variability, necessitating in-depth exploration and comprehensive analysis of the underlying adsorption kinetics. Conducting further investigations in this domain is crucial to attain a thorough understanding and optimize the overall efficiency of this intricate system.  Figure A1 presents the effect of T reg and T cond on SCE for the selected PR derivative/refrigerant pairs while maintaining the T evap = 10 • C. It has been observed that KOH6-PR/ethanol pair possesses the highest SCE among the selected PR derivative/refrigerant pairs. The SCE value ranges between 276 and 1080 kJ/kg/cycle, followed by KOH4-PR/ethanol pair (139.5-969.5 kJ/kg/cycle), SAC-2/HFC-32 pair (55.60-369.6 kJ/kg/cycle), and KOH6-PR/CO 2 (19.80-173.56 kJ/kg/cycle), respectively, while varying the T reg from 51 • C to 80 • C and T cond from 10 • C to 25 • C. In Figure A2, the effect of T cool and T evap on SCE is depicted considering T cond = 30 • C. The SCE of KOH6-PR/ethanol estimated >513.0 kJ/kg/cycle at T evap = 25 • C and T cool = 30 • C, followed by KOH4-PR/ethanol (>890 kJ/kg cycle), SAC-2/HFC-32 (>425.0 kJ/kg cycle), and KOH6-PR/CO 2 (>158.0 kJ/kg cycle). It can be concluded that KOH6-PR/ethanol is superior from the perspective of producing SCE. Figure A3 shows the variation in the COP cooling corresponding to T reg and T cond while maintaining T evap = 10 • C. The COP cooling observed sensitive for both KOH6-PR/CO 2 and SAC-2/HFC-32 whilst not sensitive for KOH4-PR/ethanol and KOH6-PR/ethanol. Figure A4 presents the COP cooling . Similarly, higher T cool placed an adverse impact on the COP cooling , as presented in Figure A4. It has been observed that, for KOH4-PR/ethanol, COP cooling value of > 2.59 is estimated followed by KOH6-PR/ethanol (>1.485), SAC-2/HFC-32 (>2.03), and KOH6-PR/CO 2 pairs, respectively.  Figure A3 shows the variation in the COPcooling corresponding to Treg and Tcond while maintaining Tevap = 10 °C. The COPcooling observed sensitive for both KOH6-PR/CO2 and SAC-2/HFC-32 whilst not sensitive for KOH4-PR/ethanol and KOH6-PR/ethanol. Figure A4 presents the COPcooling. Similarly, higher Tcool placed an adverse impact on the COPcooling, as presented in Figure A4. It has been observed that, for KOH4-PR/ethanol, COPcooling value of >2.59 is estimated followed by KOH6-PR/ethanol (>1.485), SAC-2/HFC-32 (>2.03), and KOH6-PR/CO2 pairs, respectively.        Appendix A.2. AHP for Heating Figure A5 presents the SHE that might obtained from an AHP system packed with PR derivative/refrigerant pairs. According to the obtained results, KOH6-PR/ethanol possess highest SHE potential, having value of >1955 kJ/kg/cycle at Treg = 80 °C while irrespective of the Tcond. Figure A6 shows the effect of Tcool and Tevap on SHE. It has been realized that maximum of 2744 kJ/kg/cycle of SHE can be harnessed with the AHP system packed with KOH6-PR/ethanol. Figure A7 shows the variation in the COP corresponding to Treg, and Tcond while maintaining Tevap = 10 °C. The COPheating observed sensitive for both KOH6-PR/CO2 and SAC-2/HFC-32 whilst not sensitive for KOH4-PR/ethanol and KOH6-PR/ethanol. Beyond the 65 °C of Treg, highest COPheating values are observed for both KOH4-PR/ethanol and KOH6-PR/ethanol. Figure A8 presents the COPheating of the AHP system corresponding to varying the Tcool and Tevap. It can be observed that, at low Tcool (30-35 °C), maximum SHE is produced, entailing high COPheating. The COPheating values for KOH4-PR/ethanol and KOH6-PR/ethanol are observed greater than 2.0, reflecting high heating potential.         Figure A8. Comparison of PR derivative/refrigerant pairs focusing on determining the effect of T cool and T evap on COP heating at T cond = 30 • C.